1. Field of the Invention
This invention relates generally to means for altering the exposure characteristics of a photographic apparatus when used with artificial illumination and, more particularly, to an exposure control system which is automatically actuated to change the exposure characteristics thereof in response to the coupling of a source of artificial illumination therewith.
2. Description of the Prior Art
Automatic light responsive exposure control systems are well known in the photographic arts and have been long used to control the duration of a photographic exposure. Such exposure control systems are generally utilized to control a shutter blade assembly which is movable along a predetermined path between a first position precluding scene light from reaching a film plane and a second position defining a maximum size aperture. It is often desirable to alter the operating characteristics of an exposure control system when used in conjunction with a source of artificial illumination as is more fully disclosed in U.S. Pat. No. 3,200,723, entitled "Shutter Timing Apparatus" by J. M. Topaz, issued Aug. 17, 1965. The operating characteristics of the exposure control system of Topaz are changed during the flash mode operation to reduce exposure errors which would otherwise occur as a result of the exposure control system being calibrated to operate properly under ambient conditions when the scene illumination is of substantially constant intensity. Thus when the exposure duration is controlled by a light integrating control circuit, selectively operable means are provided to reduce the amount of light required to trigger the circuit to cause termination of the exposure thereby reducing or eliminating errors in the amount of light which is allowed to impinge upon the film where the scene is illuminated by photoflash apparatus.
More recently, some exposure control systems have incorporated what is termed a "follow focus" system where the aperture adjustment is mechanically coupled with the focusing system of the camera. Thus, as the lens focus system is moved to provide the correct focus for a particular distance from the camera to the subject, the coupling mechanism of the follow focus control system also moves to provide an appropriate exposure aperture opening in response to the focusing action, thereby setting the exposure aperture in accordance with the anticipated light level at the scene to be photographed. Because of the known characteristics of the flash lamp being used, the anticipated light level at the scene to be photographed is functionally related to the distance to the subject.
An automatic exposure control system which is responsive to both scene light by way of a light integrating control circuit and to subject distance by way of a follow focus setting is described in U.S. Pat. No. 3,464,332 issued to Davidson et al. on Sept. 2, 1969. In the exposure control system of the above-cited patent, the aperture opening for admitting light to the film plane is automatically selected in accordance with the focusing of the camera and the exposure time is then controlled by a light detecting and integrating unit so as to establish a unique interrelationship between the exposure aperture and the exposure time. In systems of this type, it is preferable to provide ambient mode control solely in response to scene lighting while artificial light control is provided in response to both scene lighting and subject distance. Thus, it is important to provide scene light responsiveness which is compatible for operation in both camera modes.
Apart from the obvious difficulties in reconciling ambient and flash exposure control resulting from differences between the uniform light intensity encountered during ambient mode operation and the varying light intensity encountered during flash mode operation, other difficulties arise as a result of the operational changes in the shutter assembly between ambient and flash operation. For instance, in a two-bladed shutter assembly of the scanning type, the command trigger signal from the light integrating control circuit to terminate the exposure interval is generally received while the shutter blade elements are moving in a direction of progressively increasing effective aperture size. Thus, the forward momentum of the shutter assembly must be overcome before the blades can start to return to their closed position. Hence, a considerable overshoot is experienced where the effective aperture defined by the shutter assembly primary apertures increases beyond its value at the time that the command trigger signal is received from the light integrating circuit. Such an overshoot in the effective aperture defined by the shutter blade elements may be easily anticipated in a well known manner by configuring the photocell sweep apertures to open ahead of the shutter blade primary apertures. However, in the flash mode of operation where a source of artificial illumination is utilized, the shutter blade elements generally reach their maximum effective aperture defining position as determined by the follow focus system prior to receipt of the command signal to terminate the exposure interval. Hence, the shutter blade elements are already at rest at the follow focus setting when the command signal to terminate the exposure interval is received and thus the shutter blade elements do not overshoot their aperture defining position at the time of receipt of the command signal. Hence, the built-in anticipation for the ambient mode of operation becomes incompatible with the flash mode of operation to provide an adequate film exposure.
Therefore, it is a primary object of this invention to provide a light responsive exposure control system for photographic apparatus which system is compatible for both ambient and flash modes of operation.
It is another object of this invention to provide a light responsive exposure control system for a photographic apparatus which system is automatically actuated upon the coupling of a source of artificial illumination with the camera apparatus to provide an optimum flash mode exposure interval different from the ambient mode exposure interval.
It is a further object of this invention to provide an exposure control system for a photographic apparatus of the type having a follow focus system wherein the flash mode exposure interval before the shutter blade elements are commanded to close is automatically increased in response to the coupling of a source of artificial illumination with the camera apparatus to compensate for the reduction in shutter blade overshoot during the flash mode of operation.
It is a still further object of this invention to provide an exposure control system for a photographic apparatus operable in both an ambient and flash mode of operation wherein the exposure interval before the shutter blade elements are commanded to close during the flash mode of operation is automatically increased in response to the coupling of a source of artificial illumination so as to provide a film exposure compatible with the blade dynamics during flash mode operation.
It is an even further object of this invention to provide an exposure control system for a photographic apparatus of the type operable in both an ambient and flash mode of operation wherein the exposure control system anticipates a rather large shutter blade overshoot during the ambient mode of operation which anticipation is automatically compensated for during the flash mode of operation where such a large blade overshoot is generally not encountered.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system processing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.